Linear polyesters from p, p&#39;-sulfonyl dibenzoic acid condensed with an aliphatic ether glycol



United States l atent LINEAR POLYESTERS FROM p,p'-SULFONYL DI- BENZOICACID CONDENSED WITH AW ALI- PHATIC ETHER-GLYCOL John R. Caldwell,Kingsport, Tenn' iassignor to Eastman Kodak Company, Rochester, N. Y., acorporation of New Jersey I No Drawing. Application October 3, 1952,Serial No. 313,067

19 Claims. (Cl. 260- 75) This application relates to valuable linearpolyesters prepared by condensing a p,p'-sulfonyl dibenzoic dieste'rwith-an aliphatic ether glycol which may include some polymethyleneglycol.

It is an object of this invention to provide novel poly esters asdescribed herein. It is another object to provide a process as describedherein for preparing valuable linear polyesters. Other objects willbecome apparent hereinafter.

This application is a continuation-in-part of my copending application,Serial No. 143,594, filed February 10, 1950, now United States PatentNo. 2,614,120 dated October 14, 1952. In that application sulfonyldibenzoic acid is called his (dicarboxy diphenyl sulfone).

Highly polymeric esters of 'terephthalic acid and various glycols arewell known and have been used in the preparation of linear, highlypolymeric polyesters having properties including that of being capableof being formed into useful filaments, fibers and the like, and havinghigh melting points and a low degree of solubility in organic solvents.

Polyesters based on terephthalic acid condensed with aliphatic etherglycols of the type described below cannot be.

prepared so as to produce high melting polyesters which are of excellentutility as fibers, photographic film base, etc., inasmuch as the meltingpoint of such terephthalic polyesters would be on the order of about 120C. Moreover, the terephthalic polyesters described in the prior art donot possess the herein described highly advantageous properties whichrender them suitable for processing into shaped objects, e. g. film,tubes, etc.

It has now been found that p,p'-sulfonyl dibenzoic acid or its esters orits acid chloride can be condensed with an aliphatic ether glycol toproduce a new kind of linear polyester having highly valuable propertieswhich are superior to thoseof the linear polyesters described in theprior art. Thus, my new linear polyesters can be prepared having asoftening point above 200 C. and fibers, films, etc. of exceptionalproperties at high temperatures can be prepared from these newpolyesters. fibers, films, etc. have exceptionally high tensile strengthand elasticity. The fibers have softening points well above 160 C.(often above 200 C.) and show excel lent resistance in most organicsolvents even at elevated temperatures. My new polyesters can beextruded in the form of films or sheets which are especially valuable asphotographic film base material because of their excellent dimensionalstability and resistance to swelling by water.

These novel linear polyesters can be prepared employmg mixtures ofglycols which contain at least 30 mole percent (preferably 50 to 100mole percent) of an aliphatic ether glycol or a mixture of such etherglycols with the balance of the glycol mixture being made up ofpolymethyl'ene glycols.

My novel polyesters may contain as constituents thereof smallpercentages of man and/or m,p"iso'me'rs of These Patented May 1, 1956the p,p-sulfonyl dibenzoic compound without significant deleteriouseffect on the properties of the polyesters.

These new polyesters can be processed to form fibers by melt spinningmethods which have many advantages over the methods required forpreparing other fibers such as the acrylonitrile fibers which haverecently been commercially developedas" fibers, yarns and textilefabrics. Acrylonitrile fibers have to be prepared from solutionsnecessitating dopepreparation and solvent recovery, both of whichoperations are unnecessary in melt spinning methods. Moreover, meltspinning makes possible the more rapid spinning of fibers since nosolvent is present. The polyesters of my invention employing aliphaticether glycols can .be prepared having a relatively wide' softening rangeand good flow characteristics whereby they are quite valuable for thepreparation of shaped objectsby molding or extrusion methods. Thesoftening range and flow characteristics are improved by employingmixtures of aliphatic ether glycols with other aliphatic ether glycolsor polymethylene glycols. These novel linear polyesters can be preparedso as to soften at temperatures which are above 180-200 C. Useful linearpolyesters can also be prepared which soften at some what lowertemperatures. The polyesters having melting or softening temperatures inthe lower part of the overall range applicable to these polyesters areuseful in the manufacture of electrical insulation, gaskets, packing,flexible tubing, rods, sheets, etc.

-When the isomers of p,p'-sulfonyl dibenzoic acid diesters are employedin admixture with the p',p'-isomer, the linear polyester product has alower melting point and softening temperature. when homologs of thep,p-isorn'er and the other isomers are incorporated into, the linearpolyester. 'If homologs are employed they are most advantageously thoseof the acid, o-ethyl-p,p-sulfonyl dibenzoic acid, 'm-m ethyl-opropyl-p,p'-sulfonyl dibenzoic acid, etc. Small proportions of thevarious diesters of such isomers and homologs can be employed insubstitution for a corresponding quantity of p,p-s'ulfonyl dibenzoicacid diester when the linear polyester product is not intended to beused in the preparation of fibers. In fact, when the polyester is to beemployed for purposes other than making fibers, substantial quantitiesof these isomers and homologs can be employed 'if an exceptionally highmelting point (e. g.

over 200 'C.) is not necessarily desired but a wide soft-12.10-0-O-S0rO0-0 in wherein R1 and R4 each represents a substituentselected from the group consisting of an omega-hydroxy alkyl radicalcontaining from 3 to 12 carbon atoms and an alkyl radical containingfro'm'l to 6 carbon atoms, (B) with a dioxy compound consisting of fromabout 30 to 100 mole percent of an aliphatic ether glycol having thefollowing formula:

This same effect is produced wherein R7 represents an alkylene radicalcontaining from 2 to 4 carbon atoms, q represents a positive integer offrom 1 to 10, and R5 and Rs each represents a substituent selected fromthe group consisting of hydrogen atom and an acyl radical containingfrom 2 to 4 carbon atoms, and from about 70 to 0 mole percent of apolymethylene glycol having the following formula:

wherein 1) represents a positive integer of from 2 to 12. the dioxycompound being employed in such a proportion that there is at least anequivalent amount of oxy substituents in proportion to the carboxysubstituents .in the overall combination of the diester and the dioxycompounds, (C) in the presence of a condensing agent selected from thegroup consisting of the alkali metals, the alkaline earth metals, theoxides of these two groups of metals, the alkoxides containing from 1 to8 carbon atoms of these two groups of metals, the carbonates and boratesof these two groups of metals, lead oxide (litharge), and compoundshaving the following formulas:

wherein M represents an alkali metal, M' represents an alkaline earthmetal selected from the group consisting of magnesium, calcium andstrontium, R represents an alkyl group containing from 1 to 6 carbonatoms, R, R" and R each represents a member of the group consisting of Rand an aryl group of the benzene series containing from 6 to 9 carbonatoms and Hal represents a halogen atom, (D) at an elevated temperature,(E) the condensation being conducted in an inert atmosphere,

and (F) the latter part of the condensation being conducted at a verylow pressure of the inert atmosphere.

The dioxy compound (or compounds) is advantageously employed in such aproportion that there are from about 1.2 to about 3 oxy substituents inproportion to the carboxy substituents in the overall combination of thedibenzoic compound and the dioxy compound. Advantageously, the elevatedtemperature employed during the earlier part of the condensation is fromabout 150 C. to about 220 C. However, higher and lower temperatures canalso be employed. The upper temperature depends upon the boiling pointof the dioxy compound glycol or glycols) employed. Advantageously, thelow pressure defined under (F) is less than about mm. of Hg pressure.Most advantageously the pressure is less than about 5 mm. of Hgpressure. the dioxy compounds are aliphatic ether glycols andpolymethylene glycols having the formulas depicted above wherein R5 andR6 represent hydrogen atoms. Most advantageously the aliphatic etherglycol is used to the extent of 50 mole percent or more of the combineddioxy compounds employed.

The dioxy compounds defined above may not actually contain any freehydroxy radicals since they may be in esterified form as indicated bythe formulas given. However, these hydroxy or substituted hydroxyradicals are referred to generically as oxy radicals or substituents.The dioxy compounds which can be employed in accordance with thisinvention are most advantageously dihydroxy compounds; such compoundswill hereinafter be referred to as dihydroxy compounds although it is tobe understood that dioxy compounds of the type described above areintended to be covered by this term. Similarly, the sulfonyl dibenzoiccompounds defined above do not actually contain any free carboxyradicals since R1 and R4 are omega hydroxyalkyl or alkyl radicals;

Most advantageously 4 however, these CO--OR1 and COOR4 radicals aregenerically referred to as carboxy radicals in the description of theabove process.

Furthermore, this invention covers processes as defined above whereinthe sulfonyl dibenzoic compound is an omega-hydroxy-aliphatic diesterwhich is formed by a preliminary step comprising condensingp,p'-sulfonyl dibenzoic acid with a dihydroxy compound which is definedunder (B) and is employed in the proportions set forth under (B), at anelevated temperature, after which preliminary step the condensing agentwhich is defined under (C) is added and the condensation is completed asdefined under (D), (E) and (F). Advantageously the elevated temperatureemployed during the preliminary step is substantially that at whichreflux conditions subsist; however, higher and lower temperatures canalso be employed. Advantageously, as indicated above the polyhydroxycompound is employed in such a pro portion that there are from about 1.2to about 3 hydroxy substituents in proportion to the carboxysubstituents in the overall combination of the sulfonyl dibenzoic acidand the dihydroxy compound.

Linear highly polymeric polyesters can be prepared as described abovefrom the free acidic p,p-sulfonyl dibenzoic acid, or much moreadvantageously from its diesters by condensation with dihydroxycompounds. These linear polyesters have very high melting or softeningpoints, i. e., about 180 0-200 C. or higher and are valuable in themanufacture of sheets, films, coatings, fibers, threads, filaments,molding plastics, etc. Linear polyesters can also be prepared employingtwo or more of either of the types of glycols defined above.

The polyesters produced in accordance with this invention can beprepared which incorporate polymethylene glycols having shorter chainsthan is possible when no aliphatic ether glycol is present. Thepreparation of very high melting linear polyesters containing onlypolymethylene glycols is described in my co-pending application filed oneven date herewith, Serial No. 313,061.

The products of this invention are linear polyesters having meltingpoints on the order of ISO-200 C. (generally at least C.) which arebelow the decomposition temperature of the polyester, which polyesterscontain the following repeating unit:

wherein R7 and q are defined above. As indicated herein before, thesepolyesters can also contain up to 70 mole percent of the followingrepeating unit:

wherein p is defined above. These polyesters are capable of being formedinto fibers (such as by melt spinning methods) especially when R7represents an ethylene radical, q is l, p is a positive integer, s, offrom 2 to 8, and the mole percent of the last depicted repeating unit isfrom 30 to 70 which is in converse relation to the mole percent of thefirst depicted repeating unit which is present to the extent of from 70to 30 mole percent; these fibers canbe drawn by conventional means tofrom about 3 to 6 times their originally spun length whereby thesefibers develop strong, elastic and highly valuable properties. Valuablefibers can also be prepared employing smaller proportions (less than 30mole percent) of the last depicted repeating unit when s (or p) is a lownumber, e. g., 2 or 3. Moreover, fibers can be prepared when the soleglycol employed is diethylene glycol; however, such fibers have lowermelting and softening temperatures than those described containing ashort chain polymethylene glycol.

Examples of the aliphatic ether glycols which can be employedadvantageously in accordance with this invention include diethyleneglycol, triethylene glycol, tetraethylene glycol, bis (4-hydroxybutyl)ether, and bis (3*hydroxypropyl) ether; thus, q in the formula set forthabove is advantageously from 1 to 4, (most advantageously q is 1). Othersuitable aliphatic ether glycols having the following formulas can beemployed in addition to those mentioned above.

The ether linkages can be separated by branched chain alkyl radicals asindicated in the above formulas; however, higher melting polyesters areproduced when the various atoms in the aliphatic ether glycol constitutea straight chain. When branched chain aliphatic ether glycols areemployed, it is advantageous to combine such a glycol with a substantialproportion of polymethylene glycol in order to enhance the melting andsoftening temperatures of the polyester product. As indicated above,mono or diesters of these aliphatic ether glycols can also be employed.Thus, the acetates, propionates and butyrates are examples of suchesters. Mixtures of 2 or more of these aliphatic ether glycols can alsobe employed.

Examples of the polymethylene glycols which can be employed inconjunction with the aliphatic ether glycols in accordance with thisprocess of this invention include ethylene, trimethylene,pentamethylene, decamethylene, and other such glycols. As indicatedabove, mono or diesters of these glycols can also be employed. Thus, theacetates, propionates and butyrates are examples of such esters.Mixtures of two or more of these polymethylene glycols can also beemployed in conjunction with one or more of the aliphatic ether glycols.Generally, the more components there are in the dihydroxy composition,the greater will be the tendency toward producing a lower meltingpolyester product; accordingly, it is generally most advantageous toemploy no more than one aliphatic ether glycol and only onepolymethylene glycol in preparing any given polyester.

The catalytic condensing agents which can be employed have beendescribed above. From about 0.005% to about 0.2% of these catalystsbased on the weight of the reactants being condensed can be employed.Higher or lower percentages can also be employed. Generally, from about0.01 to about 0.06% of the catalytic condensing agent can beadvantageously employed based on the weight of the sulfonyl dibenzoicdiester being condensed.

The temperature at which polyesterification can be conducted isdependent upon the specific reactants involved in any given reaction. Ingeneral, the reaction mixture can be heated at from about 150 to about220 C. for from approximately two to three hours in an inert atmosphere(e. g. nitrogen or hydrogen); the mixture can then be heated at fromabout 225 240 to about 2803 C. in the same atmosphere for approximatelyone to two hours. Finally, the pressure can be greatly reduced to form avacuum (less than about mm. of Hg pressure but preferably on the orderof less than 5 mm. of Hg pressure) while the temperature is maintainedin the same range (225310 C); these conditions are advantageouslymaintained for approximately four to six additional hours. Theconditions can be varied considerably depending upon the degree ofpolyesterification desired, the ultimate properties sought, thestability of the polyester being produced and the use for which theproduct is intended.

The sulfonyl dibenzoic compound employed can be used in the form of itsalkyl diesters e. g. methyl, ethyl, propyl, isopropyl, butyl, etc.esters. It can also be used in the form of a partial glycol ester(omega-hydroxyaliphatic especially effective.

diester) which can be obtained by heating theacid with all: excess of adihydroxy compound of the types described a ove.

The reaction can be carried out in the presence or absence of a solvent.Inert, high boiling compounds, such as diphenyl ether, diphenyl, mixedtolyl sulfones, chlorinated naphthalene, chlorinated diphenyl, dimethylsulfolane, etc. can be used as the reaction medium.

It has been found that the type of catalyst used has an importantbearing upon the properties of the final product. Although most of thecatalysts cited in the prior art can be used, it has been found thatcertain novel catalysts give superior results. The aluminum and titaniumalkoxide complexes described in copending applications filed on evendate herewith are especially valuable for the preparation of thepolyesters described here. Moreover, novel tin catalysts have also beenfound to be See Caldwell Serial No. 313,072, Serial No. 313,078,Caldwell & Reynolds Serial No. 313,077, Wellman & Caldwell Serial No.313,074, Serial No. 313,075 and Serial No. 313,076, and Wellman SerialNo. 313,073 for a description of especially advantageous catalyticcondensing agents.

It is important to exclude oxygen and moisture at all stages of thecondensation reaction Inert atmospheres which can be advantageouslyemployed include nitrogen, hydrogen, helium, etc. During the processgood agitation is provided. Substantially anhydrous reactants can beadvantageously employed although this is not essential especially if anywater is removed in the earlier stages of the condensation.

The acid chloride of sulfonyl dibenzoic acid can also be employed, i.e., when OR-1 and OR; each represents a Cl atom. When the acid chlorideof sulfonyl dibenzoic acid is used, best results are generally obtainedby employing an exactly equivalent amount of glycol in the absence of acatalytic condensing agent. The initial temperature to start thecondensation can be about C.

in the examples given below, the hot bar sticking temperature isreferred to in several instances. The hot bar sticking test can bebriefly described as follows: The polyester fiber is placed on the fiatsurface of a heated bar and a weight of 100 g. is applied to the fiberalong a distance of inch of the fiber length. The contact surface ofthis weight has a coating of polytetrafiuoroethylene which acts as athermal insulator. The fiber is allowed to remain in Contact with thebar under this weight for one minute. The minimum temperature at whichthe fiber adheres to the hot bar under these conditions is the stickingtemperature as that term is employed in the examples given therein.

This invention can be further illustrated by the following examples; inaddition to these examples it is apparent that other variations andmodifications thereof can be adapted to obtain similar results.

Example I.'-Diethylene glycol Four hundred and twenty g. (1.0 mol) ofp,p'-sulfonyldibenzoic acid dibutyl ester and g. (1.7 mol) diethyleneglycol were placed in a reaction vessel equipped with a stirrer, shortdistillation column, and inlet for purified hydrogen. A piece ofmagnesium ribbon, weighing about 0.1 g. Was heated in iodine vapors toactivate the surface and added to the reaction mixture. The mixture wasstirred at 200-210" C. under an atmosphere of purified hydrogen until80-90 percent of the butyl alcohol had distilled off. The temperaturewas then raised to 250 C. and held for one hour. A vacuum of 1.0 to 2.0mm. of Hgpressure was applied, and heating and stirring were continuedfor 8 to 10 hours. The product obtained has an inherent viscosity of 0.6to 0.7 a. mixture of 60% phenol-40% tetrachlorethane. The crystallineform of the polyester melts at 200-210 C. When extruded in the form orfilaments and drafted, it

sticks to the hot bar at 170-180". The polymer is soluble in'y-butyrolactone, ethylene carbonate, and dimethyl sulfolane at 100-150"C. It precipitates when the solutions are cooled to room temperature.The polyester is particularly suitable for the manufacture ofphotographic film base. It gives high'strength films that show excellentdimensional stability and very low water absorption. The films can beprepared by melt extrusion methods. The polyester can also be used forelectrical insulation on wires and in condensers. It can be extruded inthe form of sheets, tubes, rods, etc.

Example 2.Bis (4-hydroxybutyl) ether Three hundred and seventy-two g.(1.0 mol) p,p'-sulfonyl-dibenzoic acid diethyl ester and 250 g. (1.5mol) bis (4-hydroxybutyl) ether were placed in a reaction vesselequipped with a stirrer, an inlet for purified nitrogen, and a shortdistillation column. A solution of 0.3 g. methyl magnesium iodide in cc.ethyl ether was added as a catalyst. The reaction mixture was stirred atZOO-210 C. until 8090% of the ethyl alcohol had distilled off. Anatmosphere of purified nitrogen was maintained in the vessel. Thetemperature was then raised to 240250 C. and held for 1.5 to 2 hours. Avacuum of 2 to 3 mm. of Hg pressure was applied and the melt stirred for8 hours. The polymer obtained softens at 160170 C. It can be extruded inthe form of sheets, rods, tubes, etc. It can be molded by injection andcompression methods.

Example 3.Diethylene glycol and pentamethylene glycol Four hundred andtwenty g. (1.0 mol) of p,p-sulfonyldibenzoic acid dibutyl ester, 106 g.(1.0 mol) diethylene glycol, and 104 g. (1.0 mol) pentamethylene glycolwere placed in a reaction vessel as described in Example 1. A solutionof 0.4 g. sodium titanium butoxide in butyl alcohol was added as acatalyst. The mixture was stirred at 200-220 C. in pure nitrogen untilabout 80% of the butyl alcohol had distilled. The temperature was thenraised to 260 C. and held for 30 minutes. A vacuum of 1.0 to 2.0 mm. wasapplied for two hours while the stirring was continued. The productobtained has a strong tendency to crystallize. It melts at 240-250 C.when in the crystalline form. This polyester is especially valuable forthe production of strong, elastic fibers by the melt spinning process.After drawing and heat treating, the fibers stick to the hot bar at210-220 C. The polyester is also suitable for the manufacture ofphotographic film base.

Example 4.-Dieth.ylene glycol and tetramethylene glycol Three hundredand seventy-two g. (1.0 mol) p,p'-sulfonyl-dibenzoic acid diethyl ester,106 g. (1.0 mol) diethylene glycol, and 72 g. (0.8 mol) tetramethyleneglycol were placed in reaction vessel as described in Example 1. Asolution of 0.3 g. potassium aluminum ethoxide in ethyl alcohol wasadded as a catalyst. The mixture was heated according to the scheduledescribed in Example 3, using a final temperature of 270275. The productobtained has an inherent viscosity of 0.80 in 60% phenol- 40%tetrachlorethane. The polyester is especially valuableas a source offibers. When melt spun and drafted, it gives fibers having a tensilestrength of 3 to 4 grams per denier and 18-25 elongation. They haveexcellent elasticity and can be dyed readily with cellulose acetatedyes. The fibers stick on the hot bar at 220230' C.

Example 5.Diethylene glycol and ethylene glycol Four hundred and twentyg. (1.0 mol) of p,p-sulfonyldibenzoic acid dibutyl ester, 150 g. (1.4mol) diethylene glycol, and 37 g. (0.6 mol) ethylene glycol were placedin a reaction vessel as described in Example'l. Magnesium turnings (0.2g.) were activated by heating with iodine and were added to the reactionmixture. Stirring at 190200 was continued until the evolution of butylalcohol was substantially complete. The temperature 8 was then raised to260-270 C. and held for 1.5 hours. A vacuum of 2.0 to 3.0 mm. wasapplied for six hours. The polyester obtained shows a relatively widesoftening range and tends to be non-crystalline. It is useful as amolding plastic. Fibers can also be prepared from this polyester.

Example 6.-Triethylene glycol and ethylene glycol A polyester having thecomposition: 1.0 mol p,p-sulfonyldibenzoic acid, 0.5 mol triethyleneglycol, 0.5 mol ethylene glycol was prepared by exactly the sameprocedure described in Example 5 except that the glycol mixture employedin the reaction consisted of 1 mole of triethylene glycol and 1 mole ofethylene glycol. The polyester obtained is useful as a molding plastic;it has a relatively wide softening range and tends to benon-crystalline.

Example 7.Dimethylene glycol and ethylene glycol One hundred andsixty-seven and two-tenths grams of the butyl ester of p,p'-sulfonyldibenzoic acid, 49.6 g. of ethylene glycol, and 41.2 g. of diethyleneglycol were admixed with 0.5 cc. of a catalyst prepared by reacting 20g. of Mg with cc. of CHaI in 250 cc. of dibutyl ether. This mixture washeated with stirring under hydrogen at 195 for 2 hours, then at 280 for1 hour, and finally under a vacuum of less than 1 mm. of mercury for 3hours. The product was a light-colored, very tough polymer which couldbe spun to a fiber which could be cold-drawn 3-400 percent and which hadan intrinsic viscosity in a 60-40 mixture of phenol-tetrachloroethane of0.6. This polyester is also useful as a molding plastic.

Example 8.Diethylene glycol A catalyst was prepared by reacting 2 gramsof magnesium with 9 g. of propyl chloride in 25 cc. dibutyl ether.Two-tenths of one cc. of this catalyst was added to a mixture of 41.8 g.of the butyl ester of p,p'-sulfonyl dibenzoic acid and 50 g. diethyleneglycol. The mixture was heated under hydrogen with constant stirring ata temperature of 200 for 5 hours, and at 250 for 1 hour. It was thenheated in a vacuum of 1 mm. of mercury for 5 hours. A polyester wasproduced which has an intrinsic viscosity in 60-40 phenoltetrachloroethane of 0.8. This product is useful as a molding resin andcan be spun into fibers.

Example 9.-Diethylene glycol and ethylene glycol The followingingredients were placed in a flask: 41.80 g. (1 mol) butyl diester ofp,p-sulfonyldibenzoic acid, 12.40 g. (2 mols) ethylene glycol and 16.96g. (1.6 mol) of diethylene glycol. In this mixture the ratio by weightof these two glycols is 0.731 which represents a mixture of glycolscontaining about 44.5 mole per cent of diethylene glycol and about 55.5mole per cent of ethylene glycol. In this mixture 0.08 g. of sodiummetal was dissolved. The mixture was then heated under a nitrogenatmosphere at 180-l90 C. for 3 hours while butyl alcohol distilled off.The mixture was then heated at 280-290 C. for 1 hour to distill off theexcess glycols. The melt was then heated at 280-290 C. under a reducedpressure of 0.05 mm. of Hg pressure for 6 to 8 hours. A hard tough resinwas obtained that softened at 230240 C. It can be melted and spun togive strong fibers that cold-draw readily.

Example 10.Diethylene glycol and ethylene glycol The procedure ofExample 9 was duplicated except that the ratio, by weight, of ethyleneglycol to diethylene glycol was changed from 0.731 to 0.933 (withoutappreciably varying the total mol proportion of ethylene glycol anddiethylene glycol employed). This represents a glycol mixture containingabout 38.4 mole per cent of diethylene glycol and about 61.6 mole percent of ethylene glycol. The result of this condensation was that aresinous product was obtained that softened at 260-270 C.

eff-44pm Example 11.-Diethylene. glycol Three hundred and six grams (1.0mol) of p,p-sulfonyl dibenzoic acid and 318 grams (3.0 mol) ofdiethylene glycol were placed in a vessel as described in Example 1.This mixture was heated at 200-210" C. with stirring until theesterification had reached substantial completion. There was then added0.3 gram of CaO as a catalyst and the mixture was stirred under anatmosphere of purified hydrogen at 200-210 C. until the distillation ofalcohol had substantially ceased. The temperature was then increased to250 C. and held for one hour. A vacuum of 0.8-1.0 mm. of Hg pressure wasapplied, and heating and stirring under the inert atmosphere werecontinued for about 12 hours. The product obtained was essentially thesame as that described in Example 1. Similar results can be obtainedusing as the catalyst: K, Ca, LizCOz, NazBOa, litharge, etc. Suchcatalysts can also be employed in the process described in the otherexamples given above after making suitable allowances for thedifferences in the reaction rates inherent in the change of thecatalyst.

What I claim is:

1. A process for preparing a linear polyester which comprises (A)condensing a p,p'-sulfonyl dibenzoic diester having the formula:

wherein R1 and R4 each represents a substituent selected from the groupconsisting of an omega-hydroxy alkyl radical containing from 3 to 12carbon atoms and an alkyl radical containing from 1 to 6 carbon atoms,(B) with a dioxy compound consisting of from about 30 to 100 molepercent of an aliphatic ether glycol having the following formula:

R50 R'1O qR7--OR6 wherein R7 represents an alkylene radical containingfrom 2 to 4 carbon atoms, q represents a positive integer of from 1 to10, and R and Rs each represents a substituent selected from the groupconsisting of a hydrogen atom and an acyl radical containing from 2 to 4carbon atoms, and from about 70 to 0 mole percent of a polymethyleneglycol having the following formula:

wherein p represents a positive integer of from 2 to 12, the dioxycompound being employed at such a proportion that there is at least anequivalent amount of oxy substituents in proportion to the carboxysubstituents in the overall combination of the diester and the dioxycompounds, (C) in the presence of a condensing agent selected from thegroup consisting of the alkali metals, the alkaline earth metals, theoxides of these two groups of metals, the alkoxides containing from 1 to8 carbon atoms of these two groups of metals, the carbonates and boratesof these two groups of metals, and litharge, (D) at an elevatedtemperature, (E) the condensation being conducted in an inertatmosphere, and (F) the latter part of the condensation being conductedat a very low pressure of the inert atmosphere.

2. A process as defined in claim 1 wherein the elevated temperature isincreased gradually during the course of the condensation up to atemperature of from about 225 to about 310 C.

3. A process as defined in claim 2 wherein the condensing agent isemployed in an amount of from about 0.005% to about 0.2% based on theweight of the sulfonyl dibenzoic diester employed.

4. A process as defined in claim 3 wherein the dioxy compound isemployed in such a proportion that there are from about 1.2 to about 3oxy substituents in proportion to the carboxy substituents in theoverall combination of the diester-s and the dioxy compound.

5. A process as defined in claim 4 wherein the elevated temperatureemployed during the earlier part of the conden-satien is from about mbout 220 C. and the low ressure defined under (F) is less than about '15mm. of Hg. pressure. I

6. A process as defined in claim 5 wherein all materials employed in theprocess are substantially anhydrous.

7. A process as defined in claim 6 wherein the major proportion of dioxycompound is made up of a cornpound having the formula:

wherein R7 and q are defined under (B).

p 8. A process as defined in claim 7 wherein the dih'ydrox compound isdiethylene glycol.

9. A process as defined in claim 7 wherein the dihydroxy compound is bis(4-hydroxybutyl) ether.

10. A process as defined in claim 7 wherein the dihydroxy compound iscomposed of an equimolecular mixture of diethylene glycol andpentamethylene glycol.

11. A process as defined in claim 7 wherein the dihydroxy compound iscomposed of about 55.5 mole percent of diethylene glycol and about 44.5mole percent of tetramethylene glycol.

12. A process as defined in claim 7 wherein the dihydroxy compound iscomposed of 70 mole percent of diethylene glycol and 30 mole percent ofethylene glycol.

13. A process as defined in claim 1 wherein the sulfonyl dibenzoicdiester is formed by a preliminary step comprising condensingp,p-sulfonyl dibenzoic acid with a dioxy compound which is defined under(B), at an elevated temperature, after which preliminary step thecondensing agent which is defined under (C) is added and thecondensation is completed as defined under (D), (E) and (F).

14. A process as defined in claim 13 wherein the me liminary elevatedtemperature is substantially that at which reflux conditions subsist,the subsequent condensation being conducted at a temperature which isgradually increased during the course of the condensation up to about280-3l0 C., and the dioxy compound is employed in such a proportion thatthere are from about 1.2 to about 3 oxy substitutents in proportion tothe carboxy and carbalkoxy substituents in the overall combination ofthe diacids, diesters and dioxy compounds.

15. A linear polyester which melts or softens below its decompositiontemperature and which melts or softens at a temperature of at least C.and contains the following repeating units:

wherein R1 represents an alkylene radical containing from 2 to 4 carbonatoms and q represents a positive integer of from 1 to 10, whichpolyester is capable of being readily formed into shaped objects withinits softening temperature range, which have excellent dimensionalstability and low water absorption characteristics.

16. A linear polyester as defined in claim 15 wherein R7 represents anethylene radical and q is 1 containing the following repeating unit:

-o-o oGsm-Qoo-om rn-o m-o-orn-orn- 17. A linear polyester as defined inclaim 15 wherein R7 represents a tetramethylene radical and q is 1.

18. A linear polyester as defined in claim 15 which contains repeatingunits in the polyester configuration in a proportion of from 30 to 100mole per cent of one of those defined in claim 15 and from 0 to 70 moleper cent of the following repeating units:

wherein p represents a positive integer of from 2 to 12.

19. A linear polyester which contains repeating units 11 12 in thepolyester configuration in a proportion of from 30 length whereby thesefibers develop strong, elastic and to 70 mole per cent of the followingrepeating unit: highly valuable properties. OOCOOz-OCOOCHEOHz-O-CH CHReferences Cited in the file of this patent 5 UNITED STATES PATENTS andconversely from 70 to 30 mole per cent of the following repeating units:2,437,046 Rothrock et al. Mar. 2, 1948 2,465,319 Winfield et a1 Mar. 22,1949 O OC SOF C O .O CH, 2,5 11 13 Dr wi et 1. Apr- 3, 1951 10 2,643,989Auspos et al June 30, 1953 wherein 5 represents a positive integer offrom 2 to 8, FOREIGN PATENTS l f WhlCh polyester 1s capab e 0 being spuninto fibers WhlCh 621,977 Great Britain p 1949 can be drawn to from 3 to6 times their originally spun

1. A PROCESS FOR PREPARING A LINEAR POLYESTER WHICH COMPRISES (A)CONDENSING A P,P''-SULFONYL DIBENZOIC DIESTER HAVING THE FORMULA: